If for example a paper processing installation is arranged after a laser printer in an automatic account processing machine, it frequently happens that the paper web leaving the laser printer has curvatures, so-called curls. These curvatures stem from the fact that the paper web is heated in the laser printer, whereby the residual moisture of the paper web is reduced. Since this heating takes place on one side, the paper curves and holds its curvature even during further passage through the paper processing machine. Since the curvature exhibits itself by interfering with the further processing it is advantageous to cancel it out by a flattening device of the kind initially referred to. However, further problems can arise from the flattening device itself. In the known flattening device, the adjustability of the support plates about their axis merely serves to alter the wrap angle with which the paper web surrounds the stationary deflecting bar, in order to thereby remove curvatures of the paper web of different degrees. The appropriate position of the deflecting bar and the deflecting roller relative to one another is determined in a trial run and then the support plates are clamped in position relative to the mount. Therefore, the deflecting bar and the deflecting roller always assume the same position, both when the paper web is running and also when it is stationary, during further operation of the machine. The disadvantage which arises from this is that the friction with the deflecting bar has to be overcome also when starting the machine. In order to avoid the paper web tearing, the starting up has to take place slowly. Also, the fact that the paper web bears in S-shape on the deflecting bar and the deflecting roller while the machine is stationary has a disturbing effect. Because of this an S-shaped deformation forms in the paper web, which can also lead to disturbance in further processing. At the least, the S-shaped deformation remains visible after the processing. Finally the curvatures of the paper web caused by the laser printer can be differently orientated. Since, however, this can only be determined after a trial run of the machine, it is frequently necessary to un-thread the paper web again from the flattening device (also called a de-curler), so that the deflecting bar and deflecting roller can be turned into a position, after releasing the clamping arrangement, in which the cancellation of an oppositely directed curvature of the paper web is possible. Then the paper web has to be threaded up again, which is time-consuming, because this does not have to take place only in the de-curler but also in further stations of the machine.
The invention is therefore based on the object of providing a flattening device for a paper web in a paper processing machine, in which S-shaped deformations of the paper web while the machine is stationary are avoided. In further development of the invention the flattening device is to be so designed that it facilitates the cancellation also of oppositely directed curvatures which are caused by the laser printer, without threading up the paper web again.
As to the first-mentioned purpose, the invention firstly provides that a servomotor is associated with one of the support plates, by means of which the support plate can be turned so far that at least the deflecting bar can be brought out of contact with the paper web.
With this novel design it is possible to avoid S-shaped deformations while the machine is stationary. Thus, each time the machine stops, the motor-driven support plate is automatically turned into a position in which at least the deflecting bar, but preferably the deflecting roller also, no longer bears on is the paper web. The flattening device is thus inactive and no S-shaped deformations can form while the machine is stationary. Also, when starting the machine, the flattening device initially remains in its inactive position. This has the advantage that no friction occurs between the paper web and the deflecting bar during starting, so that start-up can take place more rapidly. Only when the initial phase has passed is the flattening device rendered active again by motorised turning of the support plate. During the starting phase, no flattening is necessary, since the flattening device is arranged a long way from the laser printer and some time elapses before the paper web section curved in the laser printer while the machine is stationary reaches the flattening device. The flattening device can inter alia also be operated so that it is only activated when a paper section curved in the laser printer while the machine is stationary passes directly through the flattening device. For the rest of the time the flattening device remains inactive, so that wear on the smoothing device is avoided.
A particularly advantageous design of the flattening device consists in that two like flattening devices are arranged one after the other in the paper feed direction, whose support plates are adjustable about their pivotal axes by respective servo-motors so that their deflecting bars are arranged in the inactive state on opposite sides of the paper web at a distance therefrom If the paper web is threaded up in this inactive state of the flattening device between its deflecting bars and deflecting rollers, one or the other of the flattening devices can be activated after starting the machine, depending on the direction in which the paper web is curved by the laser printer while the machine is stationary.